The invention concerns in any case synthetic fibres, such as plastic fibres and absorbent fibres, such as viscose and cellulose fibres to produce a fibre web, which at least include one heat-treatment section for heating up the synthetic fibres at least to one in advance determined temperature, and at least one hydro-entangling section with liquid nozzles to aim a number of powerful liquid jets against one made of synthetic fibres and absorbent fibres combined fibre layer.
A such plant is known, where long, carded, synthetic fibres of for instance polypropylene or polyethylene are laid in a web shaped layer on the top side of a net shaped, endless wire""s upper tissue, which while running simultaneously runs in a direction, which points towards the plant""s outlet. On the same or on a following wire the fibre layer hereafter is guided through an oven, where the fibres are heated up to such a high temperature that they will be tied together with cross bonds in the affected areas.
A thermal bonding fibre layer has now been formed, serving as a framework and supporting web for absorbent fibres, such as viscose and/or cellulose fibres, which as web can be un-winded from a roller or applied in an air-flow with the help of a known forming head.
A close-meshed wire transports hereafter the supporting web with the applicated fibres through a battery of water nozzles, which send a powerful water jets down against the fibres, which hereby are driven effectively into the underlying, frame-like supporting web.
When the water jets touch the close-meshed wire, part of the water is hit back against the supporting web, with the help of which the applicated fibres are wound around the cross bonded, synthetic fibres and are laid closely against the web""s lower side, which hereby will be conveyed a smooth and flush surface.
The mentioned water exposure is in technical terms called hydro-entangling or spun-lacing. In the following the term hydro-entangling will be used.
The hydro-entangled web is dried in an oven, and finally the web is wound up in shape of a roller.
Fibre webs, which are manufactured in this way, are for instance used for products as wet wipes, towels, drapes, and gowns.
The above described process can be varied in several ways, which however has in common that they all start with a carded fibre layer. Typically the layers will be of polypropylene, polyethylene, or viscose, or a mixture of such fibres.
The carded made supporting web is soft and suitable for absorbing and intimately connect with the applicated fibres. In the longitudinal direction besides the web has such a matching strength that the process can proceed without a large risk of web breakage, which could lead to expensive stops of production and losses of materials.
Another advantage is that during the hydro-entangling process hydrogen bonds are made between the fibres, to avoid that the finished product flock and mote by use or processing.
The carding process however is slower than the following processes, which therefore cannot proceed with optimum capacity, this means the yield is reduced to a level, which is set by the carding process. Since plants of this kind are extremely expensive, it must be considered a serious lack that a great part of the known plant thus is not being used to the full extent.
Besides the carding process requiring close supervision and control, and it is difficult and complicated to work with, because for instance during running it is necessary to stretch the carded fibre layer.
The synthetic fibres, which make up the supporting web are furthermore considerably more expensive than cellulose fibres, and since the known process requires that approximately equal size quantities are being used of the two fibre types, the resulting product becomes expensive.
Even with the above mentioned content of synthetic fibres, the finished fibre web anyhow will suffer from the main lack that there exists an even big difference in the strength respectively in the longitudinal and transverse direction. The strength scale is typically 5:1. Products, which are manufactured of such fibre webs, therefore may tend to part alongside during use. Thus it is easy to stick a finger through the product.
A further disadvantage is that the known plant due to the carding process is rather unfit for production of sandwich webs, where the carded fibres become a part of several layers. The known plant can therefore not be used for production of one of today""s strongly demanded products, which consists of two non-woven fibre layers with an intermediate air-laid fibre layer, which is tied together with the two others by the help of hydro-entangling. layer, which is tied together with the two others by the help of hydro-entangling.
The purpose of the invention is to assign a plan t of at the opening mentioned character, which has a simple and cheap structure, which is easy to work with and financially favourable while running, and which furthermore can manufacture at a larger transition speed than known so far.
Another purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web with a balanced proportion between the strengths respectively in the longitudinal and transverse direction can be manufactured.
A third purpose of the invention consists of assigning a plant of at the opening mentioned character, which is designed to manufacture fibre webs taking price and features into consideration for optimum proportions between the quantities of fibre types used for manufacturing the web.
A fourth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web can be manufactured, which has a more homogeneous and precise distribution of fibres than formerly known.
A fifth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web with tighter tolerances than formerly known can be manufactured.
A sixth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a sandwich fibre web easily can be manufactured.
The new and specific, by means of which this is achieved according to the invention consist of the plant besides include an air-laying section including means during operation to generate a mainly vertical descending air-flow through at any rate the upper tissue on a mainly vertical running net shaped, endless wire, and successively supply the air-flow with at least synthetic fibres and distribute these in a smooth and homogenous, web shaped layer on the upper side of the wire""s upper tissue, which under here runs in one against the plant""s outlet pointing direction.
When the known plant""s carding process thus is replaced by a reliable and financially favourable air-laying process the plant""s remaining equipment is now made able to operate at optimum production speed, simultaneously the process becomes easy to control. The fibres can be distributed homogeneously and precisely with an equal orientation in all directions, thus the finished fibre web achieves approximately same strength in longitudinal and transverse direction, and besides manufacturing with tight tolerances becomes possible.
Now the process does not require a large strength in the longitudinal direction anymore, and the expensive synthetic fibres can among other things for this reason to a large extent be replaced by cheaper cellulose fibres, by means of which the finished fibre web""s absorbent features are improved favourably, and the cost price is being reduced.
It is especially favourable, when the absorbent fibres are added at the same time as the synthetic fibres in the same air-laying section, since the fibres hereby are mixed intimately from start, and the supporting web will be integrated in the forming process.
For the purpose a forming head can be used, which include a under the wire""s upper tissue placed suction box, which is connected t o a vacuum air pump, one above the wire placed house with one or more fibre inlets, and one in the house above the wire placed number of rotary wings for while operating to distribute the fibres in a flush layer on the upper side of the wire""s upper tissue.
A simple and cheap construction form for the plant can be constructed of a forming head for at a time to form both the synthetic fibres and the absorbent fibres, a hydro-entangling section, and an oven with sufficient high treatment-temperature to thermal bond the synthetic fibres in the affected areas.
By this construction the thermal bonding of the synthetic fibres takes place in the same oven, which is used for drying the hydro-entangled fibre web. When a specific thermal bonding oven is inserted between the forming head and the hydro-entangling section, the process can be controlled very precisely, because the temperatures in respectively the thermal bonding oven and the later drying oven can be adjusted to an optimum for the respective processes. Furthermore the fibre web is now stabilised, when it passes through the hydro-entangling process, which therefore can proceed with an optimum effect and without a large waste of loose fibres.
When the single forming head in one of the two above mentioned construction forms for the plant according to the invention is replaced with three on one-and-another following forming heads, the plant can be successfully used for production of sandwich fibre webs, since the middle forming head then mainly is supplied with for instance cellulose fibres, while the two other forming heads are supplied with synthetic fibres or both synthetic fibres and cellulose fibres.
The invention regards also a fibre web, which is manufactured by the help of the above mentioned plant according to the invention, and which contains synthetic fibres as well as absorbent fibres. Due to the production process this web has a structure with a homogenous orientation of the fibres in all directions and a good balance between the strengths respectively in longitudinal and transverse direction.
An effectively tied and therefore strong fibre web is achieved, when the synthetic fibres are bi-component fibres, which each consists of a core of at first plastic and then of another one of plastic with a higher melting point than the first. When this form of synthetic fibres are being used, bonding is secured in all places, where the fibres meet, without a simultaneous risk of the core to melt, by which the bonding feature would be lost.
With the help of the plant according to the invention manufactured fibre web can favourably have a percentage content of cellulose fibres of between 50 and 95, mainly between 60 and 90, and especially between 75 and 85, at which the web becomes substantially cheaper than the conventional fibre webs of this type.